Echo on 80M

I was talking to a local last night 12/12/2016 and at about 20:30 an echo started to appear on our signals, at one point it was so strong I had to use semi break-in because I couldn't hear what I was sending. The return echo was about the space of a dit at 22WPM, so if I sent a dit, I would dit a dit returned, so it sounded like I'd sent two dits. As I say, at one point is was so strong it was as loud as the sidetone monitor, so I had to switch from full break-in to semi break-in.

We were located about 11 miles apart and sometimes the echo was on both our signals then it faded and appeared on only one of our signals, which is strange seeing as we are only a few miles apart. This all lasted for about 10 minutes. The return echo was quite fluttery.

Conditions on 80M last night were terrible.

I've got no idea what this is, so I'm wondering if anyone else might have a theory?

My first thought is that you have two signals interfering. One direct ground wave signal and the other from the ionosphere. For that distance it would have to be an NVIS (near vertical incidence skywave) signal. Luckily, we can look at an ionosonde chart for that day and time. According to QRZ.com you are in St Albans. The nearest ionosonde is therefore Chilton, near Harwell.

The plot for 20:00hrs shows a critical frequency of 2.35MHz, but by 20:30hrs it had improved to 3.50MHz, with extensive Spread F. It then declined back to 2.550MHz by 21:00hrs. So I am pretty sure that what you heard was the direct ground wave and a strong ionospheric return from about 346km. It looks like the effect would have only lasted 10 minutes or so. The delay would have been around 2 x 346km = 692km, which at the speed of light would be about 2 thousandths of a second. You may have had additional ground reflections that would have smeared the signal out further.

You may have also had a reflection from further into the plasma cloud, so the 0.002 second could easily be double that. Anyway, that's my best guess!

Thanks for the possible explanation Steve. I have heard around the world echos before, but nothing quite like that with such a long delay and so strong as well.

On hindsight I wish I had the foresight to record it, but because I was taken back by the whole episode it didn't occur to me at the time.

At first I thought it was someone messing around till Rupert G4XRV, who I was in contact with at the time, said I had an echo on my signal that I took notice. I must say it's most off putting hearing what you've just sent coming straight back to you.

I experienced with LDE in between 2-4sec on 80m. Interesting is that I noticed it only when I used the 80x35m wire half square loop only. When I switched back to inverted V at 12m apex there was no LDE hearable at all.